1. Field of the Invention
The present invention relates a liquid crystal display device with a plurality of thin film transistors (hereinafter, referred to as "TFT-LCD device"), and more particularly to a TFT-LCD capable of repairing a point defect such as an electrical short between a pixel electrode and a data bus line of a thin film transistor (hereinafter, referred to as "TFT") during fabrication thereof, and a method for fabricating the same.
2. Description of the Prior Art
Generally, a defect in a TFT-LCD is broadly classified into two defects, one of which is a point defect occurring due to inferiority of a TFT, a pixel electrode, a pixel and the like, and the other of which is a line defect occurring due to an electrical open or short of a bus line or non-conduction of a driving IC (integrated circuit). As main defects occurring frequently in a TFT-LCD, there are an electrical short at a crossover between gate and data bus lines, an electrical short between gate and source electrodes of a TFT, and an electrical open of each of gate and data bus lines.
As a TFT-LCD becomes larger in scale thereof and higher in integration, it is necessary to solve occurrence of the above-described defects in fabrication of the TFT-LCD. Thus, a TFT-LCD with a redundancy structure or a repair structure has been developed.
FIG. 1A is a plane view of a prior art TFT-LCD with a repair structure and FIG. 1B is a cross-sectional view taken along the line A--A' of FIG. 1A.
Referring to FIG. 1A, a prior art TFT-LCD comprises a substrate 30, a plurality of pixel electrodes 34 and TFTs 31 arranged on the substrate 30 in matrix of row and column, a plurality of gate and data bus lines 33, 34, and a passivation layer 35 formed on the substrate 30 other than the pixel electrodes 34. In this TFT-LCD, the pixel electrode 34 and the TFT 31 are alternatively arranged with each other.
Also, the gate bus line 32 is extended between the pixel electrodes 32 arranged in an odd row and the other pixel electrodes arranged in an even row, and commonly connected with gates of the TFTs 31 arranged in the same row of the plurality of TFTs. The data bus line 33 also is formed in zigzag form between the pixel electrodes arranged in the odd column and the other pixel electrodes arranged in the even column and is commonly connected to source electrodes of the TFTs 31 arranged in the same column.
With reference to FIG. 1B, each of the TFTs 31 has a gate electrode 31-1 formed on a glass substrate 30, a gate insulating layer 31-2 formed over the substrate including the gate electrode 31-1, a semiconductor layer 31-3 formed above the gate electrode 31-1 with the gate insulating layer 31-2 interposed therebetween and composed of amorphous silicon, a pixel electrode 34 formed on the gate insulating layer 31-2 other than the gate electrode 31-1, an amorphous silicon ohmic layer 31-4 formed on the semiconductor layer 31-3; a source electrode 31-5 formed on the gate insulating layer 31-2 including one side of the ohmic layer 31-4 , a drain electrode 31-6 formed on the gate insulating layer 31-2 including the other side of the ohmic layer 31-4, and a passivation layer 35 formed over entire surface other than the pixel electrode 34.
Hereinafter, a method for fabricating the TFT-LCD of FIG. 1B will be described in detail.
On a glass substrate 30, a metal layer is formed by sputtering, and then patterned to form a gate electrode 31-1 and a gate bus line 32. Also, on the substrate 30 including the gate electrode 31-1, a gate insulating layer 31-2, a first amorphous silicon layer, and a second amorphous silicon layer doped with an impurity are sequentially deposited.
Next, the amorphous layers 14 is selectively etched back to form an ohmic layer 31-2 and a semiconductor layer 31-3 corresponding to the gate electrode 31-1, and then a portion of the ohmic layer 31-4 on the semiconductor layer 31-3 is etched.
Subsequently, an ITO film is formed thereon and patterned to form a pixel electrode 34. After deposition of a metal over the substrate, a photo-etching is performed, thereby allowing source and drain electrodes 31-5, 31-6 to be formed.
Finally, a passivation layer 35 is deposited thereon, and therefore the fabrication sequence of the TFT-LCD is completed.
In the TFT-LCD fabricated thus, when a signal voltage is applied to the source and drain electrodes, a channel is formed in the semiconductor layer 31-3, so that a signal voltage applied from the data bus line to the source electrode is supplied to the pixel electrode, thereby allowing the pixel corresponding to each TFT to be driven.
However, in fabrication of the above-described TFT-LCD, a metal film deposited to form a source/drain electrode and a data bus line is completely eliminated during patterning. Because occurrence of particles of the metal film, a point defect occurs between a data bus line and a pixel electrode. For occurrence of this point defect, there arises the problem that a TFT can not serve as a switching device of a liquid crystal display device.
In addition, in case that an electrical short caused by a point defect occurs in the prior art TFT-LCD device having the above-described structure, such a point defect can not be repaired therein. As a result, such a TFT-LCD device is lowered in reliability and a yield of its production is reduced.